Detergent manufacturers have long recognised the need to control water hardness to ensure adequate cleaning by detergents. The detergency builders used in the past have been of three main types, namely water-soluble sequestering builders, water-insoluble ion exchange builders and water-soluble precipitating builders. A typical precipitating builder is an alkali metal carbonate, especially sodium carbonate. Other water-soluble precipitating builders include sodium silicate (particularly effective against magnesium hardness), sodium orthophosphate and water-soluble alkali metal soaps. While from a cost point of view sodium carbonate is an attractive builder, it has at least two significant disadvantages. Firstly, sodium carbonate alone is not usually capable of reducing the calcium ion concentration in calcium hard water to sufficiently low levels to achieve good detergency under practical washing conditions. This is because crystal growth is inhibited by materials, in particular condensed phosphates, which can arise from the soiled load, or be present as contamination in the detergent composition. Secondly, the use of carbonate ions to precipitate the calcium hardness from the water can result in the deposition of calcium carbonate on the washed fabrics. It is known that the calcium carbonate precipitate is produced in such a crystal type and such a particle size that deposition on the fabrics is favoured. The presence of certain crystal growth poisons in the wash liquor can encourage this deposition. Typical such poisons are inorganic phosphates carried into the wash liquor from the soiled fabrics in cases where the fabrics have previously been washed in a composition containing tripolyphosphate.
The calcium ion concentration in a wash liquor can be reduced to sufficiently low levels by the use of, for example, a sequestering builder material such as sodium tripolyphosphate, and considerable commercial success has been achieved with phosphate-built formulations. However it has now become apparent that, under some conditions, the discharge of significant quantities of phosphates into waste waters may produce environmental problems. There is therefore an increasing desire in some countries to reduce the level of phosphorus in detergent compositions.
It has previously been thought that it was essential for precipitating builders to be substantially soluble at the temperature of use to achieve efficient water softening. With the present trend towards washing fabrics at lower temperatures with a view to saving energy costs, it has not previously been thought possible to use, as a precipitating builder material, materials which themselves are not substantially soluble in water at low temperatures. Thus, the fatty acids, which are not substantially soluble in water at room temperature, have not previously been proposed as precipitating builder materials.
We have now surprisingly found that particular fatty acids can be incorporated together with a carrier material into a builder particle and by including these particles in detergent compositions which contain an alkaline material, efficient building of calcium-hard water can be achieved, even at low temperatures.
Thus, according to a first aspect of the invention, there is provided a particulate solid detergent composition comprising:
(i) a non-soap detergent active material; PA0 (ii) an alkaline material capable of providing the composition with a pH of more than 8.0, when added to water of 12.degree. French hardness (Ca) at 25.degree. C. and at a concentration of 1.0 g/l; and PA0 (iii) at least 10% by weight of a builder material,
characterised in that said builder material is a saturated fatty acid, of which contains at least 16 carbon atoms and said fatty acid is in the form of particles having a particle size of between 50 microns and 5000 microns and comprising said fatty acid in a heterogenous mixture with a water-soluble or water-dispersible carrier material.